1. Field of the Invention
The present invention relates to a coding and decoding of binary images, and more particularly, to a method for coding and decoding scalable binary images by using modes of lower and current layers, which is capable of reducing coding modes of the binary images by considering a correlation between the lower and current layers and lessening a coding bit quantity by assigning mode coding bits according to its correlation.
2. Discussion of Related Art
The scalable shape coding has a function capable of transmitting a plurality of layers having different resolution from each other, a base layer and an enhancement layer, and decoding it. In transmitting information having a multiple of different resolutions, more information should be transmitted than in a general coding method.
In order to reduce the quantity of transmission information, a method for estimating an enhancement layer of the high resolution is applied thereto by utilizing a base layer of the lower resolution as shown in FIG. 1.
In executing the scalable shape coding for binary image information through a use of plural layers, an effective coding may be also done by employing the base layer like the aforesaid or using, on the enhancement layer, the lower layers in case several layers are constructed.
FIG. 1 shows a scalable shape coding method for general image information.
It is herewith represented only one step on an enhancement layer but the enhancement layer of several steps is generally included therein. Thus, a lower layer placed right under a current layer may be a base layer or one layer out of enhancement layers. The scalable shape coding method for binary image information has the same structure as a general scalable shape coding method.
In order to code an enhancement layer for a binary image, in case it is the enhancement layer for an intra-picture, the enhancement layer is coded by predicting its just lower layer as shown in FIG. 1. In coding a predicted-picture of the enhancement layer, the coding is performed by predicting from both of an image of the just lower layer and a previous image.
In a coding process of image information, a coding of a block unit, namely a size of 16xc3x9716, is done. In coding blocks for the binary image information, namely macro blocks (hereinafter, referred to as xe2x80x98MBxe2x80x99), an intra MB on an I-picture or a P-picture on the enhancement layer is coded by using a scan interleaving method presented on VM(Verification Model) 7.0 of the ISO/IED WG11, wherein the MB should be coded by using only its own lower layer, not using a prediction on a previous image. Its exceptional MBs are coded by using a context-based arithmetic encoding (CAE) method as a coding method of a base layer.
FIG. 2 provides a scan interleaving method.
In order to code an enhancement layer on a base layer, values of two pixels adjacent to each other on the lower and top sides are used. If two adjacent pixel values are same, there is much possibility that a pixel at a current position has the same value. Therefore, in case the two adjacent pixel values are the same and the current pixel has a value same as the two adjacent pixel values, a coding is not necessary.
In case two pixel values are different from, the pixel value at the current position should be coded and such a case is a transitional sample data (TSD). In case that the two adjacent pixel values are the same but the pixel of current position has not the same value, the coding should be also done. Such a case is an exceptional sample data (ESD). Namely, in order to code the enhancement layers by using the scan interleaving method, two kinds of data, TSD and ESD, should be coded.
To code the TSD and ESD in coding by using the scan interleaving method, information for an existence or non-existence of the ESD is first transmitted, and an applicable range of the scan interleaving is different according to an MB having the ESD and an MB not having the ESD.
FIGS. 3(a) and 3(b) provide contexts used in the CAE method.
As shown in FIG. 3(a), a context index Context_ID is decided according to a position of a context made up of neighboring pixels surrounding a coding pixel X. In order to transmit information for X and Y positions, a coding is performed by employing an arithmetic coding table previously decided according to the occurring frequency number of a context index Context_ID type which is constructed with C0 to C6.
Like this, the MB not used in the scan interleaving method is coded by utilizing a method such as a coding of the base layer, e.g., the CAE method. An inter MB on a P-picture of the enhancement, among them is coded by predicting from a previous image by using a motion vector.
In another case, namely, in case all pixels within an MB have a value of xe2x80x980xe2x80x99 or a value of xe2x80x98255xe2x80x99, only additional information, mode information such as xe2x80x9call pixels are xe2x80x980xe2x80x99xe2x80x9d or xe2x80x9call pixels are xe2x80x98255xe2x80x99xe2x80x9d, is transmitted without coding. Since the coding image herewith is the binary image, each of the pixels may have only two values as xe2x80x980xe2x80x99 or xe2x80x98255xe2x80x99. In general, xe2x80x980xe2x80x99 indicates a background and xe2x80x98255xe2x80x99 represents an object.
That is to say, in order to encode the binary images, a coding method is differently decided according to each MB, and the additional information, namely the mode information such as what coding method was used for a coding of each MB, should be transmitted. At this time, it is needed a sort for the additional information and a table for codes of the additional information, the codes being a first shape code.
The construction of the existing additional information indicating the modes for the enhancement layer of the I-picture, P-picture and B-picture is as follows.
 less than Modes of Enhancement layer on I-picture greater than 
1) allxe2x80x940: all pixels within MB becomes a background (xe2x80x9c0xe2x80x9d)
2) allxe2x80x94255: all pixels within MB becomes an object (xe2x80x9c255xe2x80x9d)
3) intra coded: If ESD (Exceptional sample data) exists, all pixels within MB are coded by using the scan interleaving method. If the ESD does not exist, only TSD (Transitional sample data) is coded by the scan interleaving method.
 less than Modes of Enhancement layer on P-picture or B-picture greater than 
1) allxe2x80x940: the same case as the above-mentioned
2) allxe2x80x94255: the same case as the above-mentioned
3) Intra coded: the same case as the above-mentioned
4) Intra not coded
5) Inter coded andand MVD=0
6) Inter not coded andand MVD=0
7) Inter coded andand MVD!=0
8) Inter not coded andand MVD!=0.
Data coded as the above is decoded as follows. The additional information indicating the modes is represented at the first position of a bitstream in each MB of the binary image. The mode information is first read on the bitstream in order to decode each of the MBs.
There is constructed a coding table for transmitting the existing additional information for the enhancement layer of the P-picture and B-picture. In such construction, in order to lessen the number of bits, the coding table is made by predicting from a lower layer or a previous image. In its construction method, the coding table is constructed by a case that a corresponding MB of just lower layer is xe2x80x9callxe2x80x940xe2x80x9d or xe2x80x9callxe2x80x94255xe2x80x9d, and by its exceptional cases.
In case a mode for the corresponding MB of the just lower layer is not xe2x80x9callxe2x80x940xe2x80x9d and xe2x80x9callxe2x80x94255xe2x80x9d, the coding table is constructed by a mode of a corresponding MB on the same layer of a just previous image.
 less than Case that the mode of corresponding MB for just lower layer is xe2x80x9callxe2x80x940xe2x80x9d greater than 
 less than Case that the mode of corresponding MB for the just lower layer is xe2x80x9callxe2x80x94255xe2x80x9d greater than 
In the existing additional information indicating the modes for the enhancement layer per each MB, the I-picture has three sorts as allxe2x80x940, allxe2x80x94255 and intra coded, and the P-picture has eight sorts as allxe2x80x940, allxe2x80x94255, intra coded, intra not coded, inter coded andand MVD=0, inter not coded andand MVD=0, inter coded andand MVD!=0, and inter not coded andand MVD!=0. If the sorts of additional information are many, the number of bits representing the respective modes becomes many, thus it means that the quantity of transmission bits is many.
FIG. 4 explains a relation between a current layer and a lower layer. Images on the current and lower layers may be same in its size. In case the size of images are different from each other, all horizontally and vertically may be different from or it may be different in only one direction. FIG. 4 shows a case different in only horizontal direction. Even though the size of images is different from, the size of each MB on all layers is constant as 16xc3x9716. Thus, in case that an image of the current layer is bigger than that of the lower layer, MBs of the current layer are included inside an MB of the lower layer, since several MBs of the current layer correspond to one MB of the lower layer. That is, an image of the current layer is down sampled and then constitutes an image of the lower layer.
As shown in FIG. 4, a size of the current layer is twice of the lower layer and an MB of the current layer corresponds to a half size of the lower layer MB in this case, the half size being a part of oblique lines in FIG. 4.
Accordingly, the present invention is directed to a method for coding and decoding scalable binary images that substantially obviates one or more of the limitations and disadvantages of the related art.
An object of the present invention is to provide a method for coding and decoding scalable binary images, using modes of current and lower layers, which is capable of improving a coding efficiency by reducing a sort of additional information representing coding methods.
Another object of the present invention is to provide a method for coding and decoding scalable binary images with modes of current and lower layers, which is capable of lessening coding modes of binary images by considering a correlation between the lower layer and the current layer and reducing the quantity of coding bits by assigning mode coding bits according to its correlation.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure as illustrated in the written description and claims hereof, as well as the appended drawings.
To achieve these and other advantages, and in accordance with the purpose of the present invention as embodied and broadly described, only one mode, an xe2x80x9cintra not codedxe2x80x9d, instead of three modes as an xe2x80x9callxe2x80x940xe2x80x9d, an xe2x80x9callxe2x80x94255xe2x80x9d and an xe2x80x9cintra not codedxe2x80x9d is used. A transmitting terminal transmits all MBs decided as xe2x80x9callxe2x80x940xe2x80x9d, xe2x80x9callxe2x80x94255xe2x80x9d or xe2x80x9cintra predictedxe2x80x9d mode, by the xe2x80x9cintra not codedxe2x80x9d mode. A receiving terminal discriminates xe2x80x9callxe2x80x940xe2x80x9d, xe2x80x9callxe2x80x94255xe2x80x9d and xe2x80x9cintra predictedxe2x80x9d from the xe2x80x9cintra not codedxe2x80x9d mode referring to pixels of the lower layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.